1. Field of the Invention
This invention relates a display apparatus and a driving method therefore wherein light emitting elements arranged in individual pixels are driven by current to display an image, and more particularly to an active matrix type display apparatus and a driving method therefore wherein the current amount to be supplied to a light emitting element such as an organic EL (electroluminescence) element is controlled by means of an insulated gate type electric field effect transistor provided in each pixel circuit.
2. Description of the Related Art
In an image display apparatus such as, for example, a liquid crystal display unit, in order to display an image, a great number of liquid crystal pixels are arranged in a matrix and the transmission intensity or the reflection intensity of incoming light is controlled for each pixel in response to image information to be displayed. While the configuration just described is similar also to that of an organic EL display unit or the like wherein an organic EL element is used for pixels, the organic EL element is, different from the liquid crystal pixel, a self-luminous element. Therefore, the organic EL display unit is advantageous in that the visibility of an image is high in comparison with the liquid crystal display unit and a backlight does not have to be provided and besides the speed of response is high. Further, the organic EL display unit is of the current controlled type wherein the luminance level (gradation) of each light emitting element can be controlled in accordance with the value of current flowing therethrough. In this regard, the organic EL display unit is much different from a display unit of the voltage controlled type such as a liquid crystal display unit.
In an organic EL display unit, a simple matrix system and an active matrix system are available as a driving system similarly as in a liquid crystal display unit. The simple matrix system has a problem in that, while it is simple in structure, it is difficult to implement a display unit of a large size and a high definition. Therefore, at present, development of display units of the active matrix type is carried out popularly. According to the active matrix system, the current to be supplied to the light emitting element in each pixel circuit is controlled by an active element provided in the pixel circuit. Usually, a thin film transistor (TFT) is used as the active element. The active matrix system is disclosed, for example, in Japanese Patent Laid-Open Nos. 2003-255856, 2003-271095, 2004-133240, 2004-029791 and 2004-093682.